Pulmonary embolism (PE) is a medical condition characterized by a blockage in a pulmonary artery, typically caused by a blood clot that has traveled from elsewhere in the body. This obstruction impedes blood flow to parts of the lung, potentially leading to health complications. Computed Tomography (CT) scans are a primary diagnostic method for identifying these clots. Timely diagnosis is important for guiding treatment decisions and improving patient outcomes.
What is a CT Pulmonary Angiogram?
A Computed Tomography Pulmonary Angiography (CTPA) is a specialized medical imaging procedure that visualizes blood vessels within the lungs. During the scan, a patient lies on a motorized table that slides into a CT scanner. A contrast material containing iodine is injected into a vein, usually in the arm, just before or during the scan. This contrast agent travels through the bloodstream, highlighting the pulmonary arteries and their branches.
The CT scanner acquires multiple cross-sectional images as the contrast flows through the lung vessels. These images are processed by a computer to create detailed views of the pulmonary vasculature. The primary purpose of this procedure is to assess the openness of these arteries and to detect blockages, such as blood clots.
How Pulmonary Embolism Appears on a CT Scan
When a pulmonary embolism is present, it appears distinctively on a CTPA scan due to the way the contrast dye interacts with the clot. Healthy blood vessels fill uniformly with the bright contrast material, appearing white or bright on the images. A blood clot, however, prevents the contrast from filling that segment of the vessel. This creates what radiologists refer to as a “filling defect”—an area within the contrast-filled vessel that remains dark or unopacified.
The appearance of clots varies by size and location. A clot may be a partial occlusion, with contrast flowing around it, or a complete occlusion, blocking the vessel entirely. Larger clots are observed centrally within the main pulmonary arteries or their lobar branches. A large clot straddling the bifurcation of the main pulmonary artery is known as a “saddle embolus.” Radiologists also examine surrounding structures like the heart chambers and lung tissue to assess the clot’s impact.
Understanding Your CT Scan Results
After a CTPA scan, images are sent to a radiologist, a physician specializing in interpreting medical images. The radiologist reviews the images, identifying filling defects or other abnormalities within the pulmonary arteries. This analysis determines the presence, size, and location of any blood clots. The radiologist also evaluates other visible chest structures, such as lung tissue and pleural spaces, for a comprehensive assessment.
Following interpretation, the radiologist generates a formal report detailing their findings. This report is sent to the referring physician who ordered the CTPA. The referring physician discusses these findings with the patient, explaining whether a pulmonary embolism has been confirmed or ruled out. This discussion covers the results’ implications and helps determine the next appropriate steps, which may involve further evaluation or medical management.